The invention relates to a process for operating a combined gas turbine/steam turbine installation with an integrated partial fuel-combustion process, wherein a part of the compressed combustion air is fed via a heat exchanger and a booster compressor to a gasification reactor in which a fuel is gasified, whereupon the crude gas produced is cooled in a boiler and purified and finally the pure gas is fed to the combustion chamber of the gas turbine, and wherein, moreover, saturated steam generated in the boiler is passed to the superheater of a waste heat steam generator which is charged with the off-gas from the gas turbine.
Processes of this type are applied for the production of fuels which, on combustion after purification, correspond to the currently applicable regulations with respect to atmospheric pollutions. For this purpose, a sulphur-containing fuel, for example heavy oil, is gasified in a pressure reactor, for which purpose a part of the combustion air compressed in the compressor of the gas turbine installation is utilized, and is subsequently brought in a preparation plant to a high degree of purity. The gasification is a very high-temperature process, and for this reason the gas is cooled, before purification, in at least one boiler which is charged with preheated feed water from the steam water circulation and in which, by means of the heat removed from the gas, saturated steam is generated which is subsequently superheated in the waste heat steam boiler up to the state of fresh steam and is fed to the steam turbine.
A process of the type mentioned is described and diagrammatically represented in the booklet by BBC Brown Boveri Nederland BV No. NL-BBN 201N under the title "milieuvriendelijke energie-opwekking onder toepassing van vergassing van sterk zwavelhoudende vaste en vloeibare brandstoffen [Generation of Energy, without Pollution of the Environment, with the Use of Gasification of Solid and Liquid Fuels of High Sulphur Content]". The heat removed in the heat exchanger from the compressed combustion air is utilized in this installation for a modest heating of the pure gas, before the latter is fed to the combustion chamber of the gas turbine. A disadvantage is here that the relatively small quantity of heat restricts the extent of preheating of the fuel gas.
A process described at the outset has also been disclosed in the booklet ASME Publication 75-GT-73 under the title "Process Systems for Conversion of Difficult Fuels to Synthetic Fuels for Baseload Gas Turbines". In this process, the air passing to the booster compressor is recooled in an air cooler, the heat obtained not being reintroduced into the cycle and thus representing an energy loss.
In the two known solutions, it is moreoever possible that the saturated steam which is generated as the result of cooling the gas and which is under a high pressure, contains moisture which must be segregated in a water separator before the steam enters the superheater part of the waste heat steam generator. Under the prevailing pressures, it is no longer possible to dry saturated steam by letting it down from a higher pressure to the superheater pressure; the result of this would only be a further increase in the wetness of the steam.
It is the object of the invention to avoid these disadvantages and to increase the total efficiency of a combined gas turbine/steam turbine installation of the type mentioned at the outset.
According to the invention, this is achieved when the saturated steam is dried and pre-superheated in the heat exchanger.
The advantages of the invention are in particular that, on the one hand, the heat stress at the delivery of the booster compressor is restricted to admissible values by the recooling of the compressed gasification air and that, on the other hand, the pre-superheated steam can by-pass the high-pressure drum of the waste heat boiler and the water separator thereof. Since only a part of the working medium of the steam turbine has the flow through these items of equipment, the latter can be designed to have smaller dimensions and thus to be more economical.